Definition & Overview
A fistula is an abnormal connection between two hollow spaces, organs, or between an organ and the body surface. Fistulas can develop in any part of the body and they can either be congenital (present at birth) or caused by an injury, inflammation or infection. In the case of an arteriovenous fistula, there is an abnormal connection between an artery and a vein. This presents a huge problem because the arteries carry oxygenated and nutrient-rich blood from the heart to the capillaries and veins. The veins, on the other hand, transports oxygen-deficient blood to the heart for re-oxygenation.
When an arteriovenous fistula develops, it interrupts the normal physiological process in as much as the normal blood flow is concerned. The blood flows from the arteries to the veins bypassing the many small capillaries that provide nutrients and oxygen to other tissues and organs of the body.
Who Should Undergo and Expected Results?
Patients with arteriovenous fistulas must seek treatment as soon as possible.
Just like other types of fistulas, an arteriovenous fistula can also be congenital and usually develops in the head and neck, liver, legs, and spine.
Patients with arteriovenous fistulas in the head and neck experience abnormal pulsations. The presence of fistulas in the head region can cause serious heart problems unless they are treated early on.
If the arteriovenous fistula develops in the lungs, patients can experience coughing of blood and clubbing of fingers. Their skin also has a bluish colour, which indicates that they are not getting enough oxygen. If present in the gastrointestinal tract, the condition can cause bleeding.
Some symptoms or signs that a patient has fistulas are:
- Bulging, purplish veins that are visible on the surface of the skin
- Overall feeling of fatigue
- Heart failure
- Decreased blood pressure
Patients need to see a doctor if any discomforting symptoms manifest and worsen. Early detection and treatment of fistulas can help prevent complications and further damage to nearby tissues and organs.
If not treated early, arteriovenous fistulas can cause mild to serious complications, including the following:
Blood clots - Arteriovenous fistulas can cause blood clots that could lead to deep vein thrombosis, a localised blood clot that can clog the heart, lungs, and brain. In serious cases, this condition can cause a stroke.
Heart failure. When a fistula develops, the blood flows more vigorously into the new direction than it would if it goes to its original route, which is arteries-capillaries-veins. Because some parts of the body are not getting enough oxygen, the heart would exert more effort to compensate by pumping harder. Eventually, this can weaken the heart’s muscles and its walls leading to heart failure heart failure.
Bleeding - The presence of arteriovenous fistulas can cause bleeding in parts of the body where they are located. These include the legs, gastrointestinal tract, heart, neck, and head.
How is the Procedure Performed?
Upon the presentation of symptoms, the doctor will conduct a physical examination with the use of a stethoscope to “listen” to the areas of the body where an arteriovenous fistula is suspected.
Arteriovenous fistulas produce a characteristic sound indicating that the blood no longer follows a normal pathway. If this sound is observed, additional tests will be performed to confirm the condition. These include:
- Computed tomography (CT) angiogram - The patient is injected with a dye that functions as a marker. This marker is detected in a CT scan helping doctors to locate the fistula.
- Duplex ultrasound – This uses a transducer that emits high-frequency sound waves that bounce off when they hit the red blood cells. The frequency by which these waves bounce and all other considerations help determine the presence of a fistula in the suspected area.
- Magnetic resonance angiography (MRA). This diagnostic test is used for deep-seated fistulas. It functions more like a magnetic resonance imaging (MRI). It uses a special dye, a magnetic field, and radio waves to create an image of the arteriovenous fistula and its exact location.
As for the treatment, there are many options depending on the severity of the fistula as well as its location and other factors such as the patient’s health and age. These options include:
- Catheter embolisation – This is a simple technique where a catheter is guided to the fistula. A coil or a stent (a small mesh tube used for small arteries, especially weak ones) is used to reroute the blood flow to the original pathway.
- Ultrasound-guided compression. This option is rarely used but is effective in more than 30% of patients reported to have a fistula. In this treatment, an ultrasound probe is used to compress the fistula, bringing the blood flow back to the original pathway.
- Surgery - Large arteriovenous fistulas require a more aggressive treatment such as surgery. The type of surgery is dependent on the size and location of the fistula.
Possible Risks and Complications
Various treatment methods used to repair arteriovenous fistulas come with risks and possibility of complications. Catheter embolisation’s possible complications include stroke-like symptoms. On the other hand, surgical procedures for the treatment of this condition are associated with bleeding, risk of infection, and allergic reaction to anaesthesia.
Mayo Clinic; “Arteriovenous fistula”; http://www.mayoclinic.org/diseases-conditions/arteriovenous-fistula/basics/tests-diagnosis/con-20034876
Mounta Sinai Hospital; “Arteriovenous fistula”; http://www.mountsinai.org/patient-care/service-areas/neurosurgery/areas-of-care/cerebrovascular-center/arteriovenous-malformations/arteriovenous-fistulas